In the manufacture of bevel and hypoid gears with curved flank lines, the cutting tools utilized are primarily face mill or face hob cutters, such types of cutting tools are well known in the art of gear manufacture. In face mill cutters, the cutting blades are arranged about the face of the cutter head in a circle such that one tooth slot is formed with each plunge of the cutter and the cutter must be withdrawn and the workpiece indexed to the next tooth slot position in order to form the next tooth slot. In face hob cutters, cutting blades are arranged about the face of the cutter head in groups with each successive blade group cutting a successive tooth slot such that with a single plunge of the cutting tool, and accompanying rotation of the workpiece in a timed relationship with the cutting tool, all tooth slots of the workpiece are formed.
Cutting tools for face mill and face hob processes usually consist of disk-shaped cutter heads with stick-type (also known as bar-type) cutting blades, made from bar stock tool steel or carbide for example, which are inserted into and positioned in mounting slots (i.e. slots) formed in the cutter heads. The slots generally extend between the opposed faces of the cutter head and may be oriented parallel to the cutter axis of rotation or at a predetermined angle thereto. Each cutting blade comprises a front rake face, cutting edge, a cutting side surface oriented at a predetermined relief angle, clearance edge, clearance side surface, and a top surface. Examples of inserted stick-type cutter heads and blades are shown in U.S. Pat. No. 4,575,285 to Blakesley, U.S. Pat. No. 4,621,954 to Kitchen et al. and U.S. Pat. No. 5,890,846 to Clark et al.
The disk-shaped cutter head body is divided into blade groups or “starts” with each blade group containing one to three slots. In the case of one slot per group, the cutter may form the entire tooth slot, or the cutter is dedicated to cut only the convex or concave tooth flanks of a workpiece usually as a finishing operation. In the case of two slots per blade group, there is an inner and outer cutting blade located in each group for cutting the convex and concave sides of a tooth slot. Such a cutter head can be designed as a roughing cutter, a finishing cutter, or a “completing” cutter which roughs out the tooth slot and finishes convex and concave tooth flanks at the same time. In the case of three slots per blade group, the additional cutting blade is usually a “bottom” or roughing blade. The bottom blade can be arranged as an inner or outer blade (convex or concave cutting, respectively). With this shape, the third blade reams out the root fillet of the tooth slot and supports the cutting action of one of the two other blades.
In building a cutter, cutting blades are inserted into the appropriate slots of a cutter head and are then trued by positioning each blade at a certain uniform blade height relative to the cutter head. This may be done by moving a blade along the lengthwise direction of the slot until a predetermined distance (i.e. height), such as from the blade tip to a reference location on the cutter head, is attained. Once the desired height is achieved, the cutting blade is clamped via a clamping mechanism which usually comprises one or more clamping screws exerting force which directly or indirectly presses and holds the cutting blade in position in its respective slot. It should be noted that when building the cutter, the inserted blades may be clamped with a holding force which is just sufficient to prevent each blade from falling from its respective slot. For truing, the holding force is lessened by an amount whereby the blades are movable for truing.
In some instances, a uniform radial location of the cutting edges of the cutting blades is the most important aspect of a cutter. This may be determined by a truing procedure wherein the cutting blades are first axially positioned to a uniform height with respect to the cutter head. The cutting edge of each blade is then located by a probe (contacting or non-contacting type) to determine the radial location of a same predetermined point on each cutting edge. The radii differences between the blades are used to calculate a value to move the blades in either direction (plus/minus) in the lengthwise direction of the slot thereby effecting a radial shift in the position of the cutting edge with the result being all cutting edges following essentially the same path as the cutter is rotated about its axis. The axial location (i.e. height) uniformity of the end point of the cutting blades is lost due to the axial adjustment necessary to effect the cutting edge shift. However, the differences in the heights of the blade tips usually remain within pre-set tolerances.
In the cutter truing machine of U.S. Pat. No. 5,839,943, it is disclosed to push a cutting blade in the lengthwise slot direction until a stop surface is encountered by the tip of the cutting blade thus establishing a uniform height for all cutting blades in a cutter head. However, the impact of the blade tip with the stop surface may result in damage to the cutting blade. Furthermore, if the stop surface is not correctly set and the desired blade height is exceeded, the machine is incapable of moving the cutting blade in the opposite direction along the slot.
In the cutter truing machine of U.S. Pat. No. 6,568,884, truing is effected by a stable arm having a push head for pushing on a cutting blade so as to move the cutting blade in the direction of its respective slot in a cutter head and a probe for measuring the height of each cutting blade relative to the cutter head. However, if the desired amount of blade movement is exceeded, the machine is incapable of moving the cutting blade in the opposite direction along the slot since the push head is capable of pushing the blades only in one direction. Also, with the probe and push head both mounted on the same arm, high pushing forces may affect the fragile mechanisms of the arm.